Various automobile accessory assemblies including, for example, a water pump, an alternator/generator, a fan for cooling coolant, a power steering pump, and a compressor, may be driven using the vehicle engine. In particular, a driving pulley actuated by an engine shaft of the motor vehicle drives an endless drive belt that in turn drives the accessory assemblies through driven pulleys. The endless drive belt, the various pulleys, and a tensioner pulley assembly may be referred as an accessory drive system.
Periodic torque pulses initiated by, for example, combustion engine tiring may create significant speed transitions. These speed transitions may interrupt smooth operation of the driven components of the accessory drive system. In addition, inertial and driven speed transitions associated with startup, shutdown, and gear shifting may also interrupt operation of the driven components. These transitions can result in undesirable effects such as, but not limited to, endless belt jump, endless belt wear, bearing wear, and noise.
Overrunning alternator decouplers (OADs) may be used to dampen torque variations and speed transitions. An OAD is installed on the alternator of the accessory drive system, as the alternator usually has the highest inertial load of the accessories driven by the endless drive belt. The OAD has decoupling capabilities, and also provides torsional isolation to the alternator. By decoupling larger inertial components from the system, such as the alternator, issues such as endless belt wear, endless belt noise, bearing life, and movement of a tensioner arm may be improved.
Although OADs may improve noise as well as the life of the various components of the accessory drive system, several drawbacks currently exist. For example, OADs may introduce additional cost due to part complexity and packaging space in an accessory assembly. This makes it challenging to use un OAD in some applications. Moreover, some types of OADs may be especially susceptible to contamination or heat. Finally, some types OADs may have issues with noise, torque consistency, low hysteresis, or smooth spring rate.